The proposed work involves the utilization of long-term and short-term monolayer cultures of normal and neoplastic mammary cells to determine precisely the action of hormones on differentiation and secretory function of normal breast tissue and the manner in which they may regulate the growth of mammary neoplasms. The synthesis and secretion of milk components (proteins, carbohydrates and lipids) will be assessed by various biochemical techniques. Morphological criteria by electron and light microscopy will be established in the classification of hormone responsive normal and neoplastic cells. Studies will be carried out to evaluate the steps at which hormonal alterations in cell metabolism are regulated and to biochemically define these regulatory mechanisms. Studies to evaluate the involvement of cyclic AMP metabolism will be included.